Interference or decay over short retention intervals

It is well established that if a formally noninterfering task which minimizes rehearsal is interposed between presentation and recall of a short consonant sequence, recall lessens as retention interval is increased. Superficially, this appears to be a classical example of decay. Keppel and Underwood have proposed an alternative explanation in interference-theory terms suggesting that forgetting in this paradigm is due to proactive interference from extinguished associations from prior trials which recover during the retention interval. An experiment was carried out which varied retention interval after four consonants had been presented. More forgetting occurred as a result of the longer interval, but the main dependent variable was the nature of “intrusions.” For neither the short nor long interval were wrong letters equiprobable, errors tending to be acoustically similar to the correct letter. But the distribution of long-interval errors tended more towards random than did that for the short interval. It is argued that the difference in error distribution between short and long interval is incompatible with the Keppel and Underwood explanation. A modification of decay theory is proposed which regards decay as a loss of discriminative characteristics (in the present case acoustic), and recall as a process involving discrimination of available traces. This model would be supported by the error-distribution data.